The major thrust of this study is to elucidate the molecular genetics of neoplastic transformation of normal tissues. Two experimental systems were used: 1) Two rat leukemia helper viruses - a) KSV(RHHV) originally isolated in this laboratory and b) WR-RaLV, a wild rat tumor virus. 2) Intracisternal A particle from BALB/c mammary tumor cell line and plasma cell tumor, MOPC-104E. Multi-disciplinary approaches involving nucleic acid and protein chemistry and tissue culture were employed in this investigation. We have earlier completed extensive characterizations morphologically, biologically, biochemically and immunologically of these retraviruses. Our current interests focus on the molecular mechanisms involved in the evolution of a transforming DNA sequence through the recombination between a rat leukemia helper virus DNA sequence and rat endogenous DNA sequence. Our total research efforts are concentrated on: 1) Molecular cloning and recombinant DNA analysis of RaLV and KSV DNA sequences, 2) Restriction endonuclease mapping of the cloned viral DNA sequences, 3) Functional organization of the viral genome, 4) IAP specific DNA sequence in DNA of human chondrosarcoma carried in nude mouse.